土壤質地對美國螯蝦行為與棲地偏好之影響

Abstract

美國螯蝦(Procambarus clarkii)為典型的淡水螯蝦入侵物種，具有雜食性、易繁殖及生長迅速的特徵，對台灣原生生態有相當大的衝擊。因此，瞭解美國螯蝦行為受環境因子之影響更顯重要。過往研究大多僅針對美國螯蝦在不同土壤質地上挖掘行為，而未探討該生物於不同土壤質地之活動情況。本研究主要針對不同底質與美國螯蝦之關係進行實驗。 研究分成兩部分，第一部分為針對美國螯蝦在砂土及壤土上之移動軌跡以碎形理論分析。當碎形維度值較接近1顯示美國螯蝦的移動是趨於直線，有明確目標；但在維度值接近2時則表示移動狀況複雜，無明確移動之目標。研究結果顯示雄螯蝦在壤土底質上之碎形維度值約為1.10-1.50，砂土底質上則為1.10-1.40；雌螯蝦在壤土底質上大多落於1.10-1.80，砂土底質為1.10-1.70之間。 另比較美國螯蝦在不同底質上其碎形維度值與各種行為進行研究分析，結果顯示雄螯蝦的移動不受底質及行為影響，碎形維度值為1.10-1.50。而雌螯蝦則受底質及行為之影響，當移動距離、移動瞬間速度、佇立或行走行為所佔之時間百分比改變，碎形維度值亦會跟著變化。但雌螯蝦在壤土上之移動不受挖掘行為或螯行為的影響，不過在砂土上卻會因此其而有所變化。 第二部分則是針對不同底質之偏好選擇情況進行研究，結果顯示美國螯蝦對土壤質地有選擇性，在試驗中，美國螯蝦大多會選擇壤土底質活動及棲息，較少出現於砂土及砂質壤土的混和土上。根據此結果，美國螯蝦對土壤具有選擇性，可提供為控制該外來種生物分布之參考方法。

Red swamp crayfish, Procambarus clarkii, is a typical invasive freshwater crayfish species and has been widely distributed in north Taiwan and Yilan County. Crayfish have some features that include omnivory, high fecundity, and rapid growth rate, often resulting in the great impacts on local ecosystem. Published red swamp crayfish studies are mainly focused on changes of burrowing behavior in different soil textures. In this study, we aim to know the relationship between different soil texture and crayfish behavior. We investigated that the fractal dimension of crayfish’s movement in loam and in sand. The fractal dimension, clossing 1, showed the movements of crayfish which were clossing straight with indefinite target. As for clossing 2, it showed moving trace were complex and with no target. The results showed that the fractal dimension of male crayfish in loam and in sand were in a range of 1.10-1.50, and 1.10-1.40 and for female crayfish, 1.10-1.80, and 1.10-1.70. The male crayfish was not clearly trended to the relationship between the fractal dimension and behaviors. Furthermore, movement of male crayfish didn’t change in different soil, as fractal dimension ranged 1.10-1.50. The female crayfish clearly trends to the relationship between the fractal dimension and moving distance, Instantaneous movement speed, standing or walking. The relationship between the fractal dimension and Chelating behaviors or burrowing behaviors of the female crayfish didn’t influence in loam, but did in sand. The experiment was focus on understanding the habitat preference of the red swamp crayfish. Results indicated that the crayfishes primarily occupied the loam during the 6-hr test period instead of other soils, such as the sand or sandy loam. It also suggested that soil texture may influence red swamp crayfish distribution and, therefore, could be served as one approach of invasive crayfish control strategies in Taiwan.